JFM-19-S-0921.R2 final version.pdf (10.88 MB)
Salient three-dimensional features of the turbulent wake of a simplified square-back vehicle
journal contribution
posted on 2020-01-23, 15:08 authored by Giancarlo Pavia, Martin Passmore, Max Varney, Graham HodgsonIn this paper, the unsteady wake of a simplified square-back vehicle, with and without wheels, is investigated using large scale Tomographic Particle Image Velocimetry (TPIV), at a Reynolds number of ReH = 5.78 · 105 (based on the model height). In the no-wheel case, the time averaged wake features a balanced toroidal shape, with a good level of symmetry in both vertical and lateral directions. However analysis of the wake dynamics shows this widely accepted result to be a poor model of the wake structure. Application of Proper Orthogonal Decomposition (POD) to the unsteady data reveals the existence of the widely reported bi-stable behaviour, consisting of random switches between two
lateral symmetry breaking states. For the first time, the 3D topology of each state is fully characterised and the changes in wake topology during the switches between bistable states are also described. Each symmetry breaking state is shown to feature a characteristic ‘hairpin vortex’ structure that is the result of the merging of two horseshoe vortices, aligned with the vertical edges of the model base. The mutual interactions between these vortices are found to be at the origin of the bi-stable mode. The vertical symmetry is lost when wheels are added to the model, resulting in the formation of an upwash dominated wake. The bi-stable behaviour is removed but considerable mobility in the near-wake remains, in the form of a swinging motion of the rear recirculation.
Funding
Inst Sp - Feasibility studies in the application of Tomographic PIV to vehicle drag reduction - EPSRC Institutional Sponsorship Martin Passmore : EP/P511195/1
(EPSRC) Special Interest Group in Ground Vehicle Aerodynamics : Nick Daish
History
School
- Aeronautical, Automotive, Chemical and Materials Engineering
Department
- Aeronautical and Automotive Engineering
Published in
Journal of Fluid MechanicsVolume
888Publisher
Cambridge University Press (CUP)Version
- AM (Accepted Manuscript)
Rights holder
© The AuthorsPublisher statement
This article has been published in a revised form in Journal of Fluid Mechanics https://doi.org/10.1017/jfm.2020.71. This version is published under a Creative Commons CC-BY-NC-ND. No commercial re-distribution or re-use allowed. Derivative works cannot be distributed. © The Authors.Acceptance date
2020-01-21Publication date
2020-02-17Copyright date
2020ISSN
0022-1120eISSN
1469-7645Publisher version
Language
- en